Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$111.62	10.359%	$123.1827	$123.18	$123.20	$123.20
Purchase #2	$212.84	7.861%	$229.5714	$229.57	$229.55	$229.60
Purchase #3	$131.32	7.460%	$141.1165	$141.12	$141.10	$141.10
Purchase #4	$67.45	7.295%	$72.3705	$72.37	$72.35	$72.40
Purchase #5	$59.55	13.867%	$67.8078	$67.81	$67.80	$67.80
Purchase #6	$199.73	7.646%	$215.0014	$215.00	$215.00	$215.00
Purchase #7	$65.29	11.797%	$72.9923	$72.99	$73.00	$73.00
7 purchase totals =	$847.80		$922.0426	$922.04	$922.00	$922.10